A storage battery is a kind of power supply widely used in industrial manufacturing, transportation, telecommunication, etc. In order to detect power failure or insufficient capacity of a storage battery in advance, and to avoid potential accidents thus caused, there is a need for a full test of operating parameters of the battery. Generally, the working state of a battery can be evaluated by measuring the battery resistance. Currently, commonly used methods for measuring battery resistance include the density method, the open circuit voltage method, the direct current (DC) discharging method, and the alternating current (AC) injection method.
For an Uninterrupted Power Supply (UPS) system, the voltage of a battery bank usually ranges from 400V to 600V. However, conventional devices for measuring battery resistance can only measure voltages lower than 60V. If the voltage across the two electrodes of a battery to be tested (“the subject battery”) is too high, or if the current in the circuit is too large, the measuring device may be damaged. For example, an AC current source may be broken due to an over-current in an AC injection circuit when measuring battery resistance using the AC injection method. Even if the AC current supply is protected by a fuse, frequent replacement of broken fuses due to the over-current may be required.
Moreover, in addition to the battery resistance, it may be desirable to measure other parameters of a battery, such as the voltage or load current of the entire battery bank, using the same measuring device without changing its testing probes when measuring the working state of the battery. Since conventional devices for measuring battery resistance are not able to measure high voltages across the battery bank, a user usually needs to use two different measuring devices, one for measuring battery resistance, and another for measuring high voltages across the entire battery bank. Such operation makes the measurement process less convenient.
Thus, there is a desire for a battery tester capable of measuring both an internal resistance and a high voltage of a storage battery bank, that can switch between different measurement functions easily, and can provide protection for circuit components and prevent damage to the battery tester under high voltage/large current conditions.